“ASTMH has a long history of scientists and physicians working on mosquito-borne diseases … It will be important to expand these studies of Zika virus into the Americas.” – Kathryn A. Hanley, PhD, ACAV Chair
Kathryn A. Hanley, PhD, American Committee on Arthropod-borne Viruses (ACAV) Chair, Adjunct Associate Professor at the University of New Mexico School of Medicine and Adjunct Associate Professor at the University of Texas at El Paso. The Hanley Lab at New Mexico State investigates the molecular biology, evolution and ecology of emerging RNA viruses like dengue and influenza, with the goal of using this basic knowledge to design better methods to control their spread.
Stephen J. Thomas, MD, FACP, FIDSA, FASTMH, serves as the Deputy Commander for Operations at the Walter Reed Army Institute of Research (WRAIR). He also sits on scientific advisory committees and boards for the Department of Defense, NIH, non-governmental organizations, and numerous pharmaceutical companies working on flavivirus vaccine development efforts. In addition, he is a member of the WHO’s Dengue Vaccine Working Group advising the Strategic Advisory Group of Experts (SAGE) on immunizations.
What is Zika virus? Where did it originate and how has it spread?
Dr. Thomas: Zika virus (ZIKV) is a flavivirus of increasing global public health importance. ZIKV is in the same family as West Nile virus, yellow fever virus, the dengue viruses, and Japanese encephalitis virus. As with many of the flaviviruses, ZIKV is most often transmitted to humans as a ZIKV-infected
Aedes mosquito takes a blood meal. ZIKV can also be transmitted from a woman to her fetus during pregnancy and there are concerns it may be transmitted sexually or through contaminated blood products.
Historically, ZIKV transmission and disease outbreaks have occurred in areas of Africa, Southeast Asia and the Pacific Islands, and recently there has been a significant outbreak in the Americas. The first locally transmitted ZIKV in Brazil was reported in May 2015. Since that time, transmission has expanded greatly, not only in Brazil but throughout the region in Barbados, Bolivia, Brazil, Colombia, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Saint Martin, Suriname and Venezuela. In December 2015, Puerto Rico reported its first locally transmitted case. ZIKV infection has also been reported in the United States in returning travelers.
Dr. Hanley: In light of the successful invasions of yellow fever, dengue, chikungunya and West Nile virus into the Americas, it was not a great surprise that, in April of 2015, illnesses caused by Zika virus were identified in Brazil. Moreover, since Zika virus shares the vector of yellow fever, dengue, chikungunya virus, there was obvious concern that the virus could become established and spread. Since its introduction in the Caribbean in 2013, chikungunya virus has spread throughout the Americas and caused over 1.7 million cases.
How much do we know about Zika virus?
Dr. Thomas: What we know about ZIKV infection and disease has largely been learned from the study of recent small outbreaks, but much remains unknown. The majority of people who are infected are thought to not experience clinical symptoms or experience very mild symptoms. It may not be possible to make a clinical diagnosis of Zika disease based on symptoms alone because of the similarity between Zika and other viral diseases such as dengue and chikungunya, all of which are transmitted by the same mosquito species in similar geographic regions. If a ZIKV infection is suspected there are tests available to diagnose infection depending on when in the course of the infection the patient seeks medical care.
Trends with the current ZIKV outbreak in the Americas include an increase in the rate of Guillain-Barré syndrome (GBS) and the occurrence of congenital microcephaly and fetal losses among women infected with ZIKV during pregnancy. GBS is a symmetric and progressive development of muscle weakness that occurs following infection and may become severe requiring advanced medical care. GBS typically spontaneously resolves but may have a prolonged and serious course. Congenital microcephaly is when a child’s head size is smaller than normal and this often also means there is concurrent microencephaly or a smaller than normal brain. Children with microcephaly may be developmentally delayed and intellectually disabled. When microcephaly results from a congenital infection the prognosis may be poor. Although there is a strong association between ZIKV infection and increased incidence of microcephaly, direct causality has not been established.
What can people do to prevent Zika virus infection?
Dr. Thomas: The best prevention against acquiring a ZIKV infection is to avoid the mosquitoes that can transmit the virus. Avoiding unnecessary travel to areas with active ZIKV transmission is recommended, especially for pregnant women or women attempting to become pregnant. If travel is unavoidable, individuals should use personal protective measures to avoid mosquitoes such as applying approved repellants to exposed skin or clothing and wearing long sleeves and pants limiting exposed skin. Staying in air-conditioned rooms or rooms with screens on the windows or sleeping under a bed net will help to limit your exposure to mosquitoes. There are no licensed vaccines to prevent ZIKV infection or disease but a number of groups are working to develop potential candidates. Vaccines against other flaviviruses have been successfully licensed for use so it is plausible a ZIKV vaccine could be developed.
So, what’s the next step?
Dr. Hanley: ASTMH has a long history of scientists and physicians working on mosquito-borne diseases, with members in two subgroups: ACAV and the American Committee Medical Entomology (ACME) possessing substantial international expertise in this area. Notably, members of ACAV have participated in epidemiological investigations of Zika virus outbreaks in Micronesia and Brazil, established a molecular and serological diagnostic pipeline in Brazil, conducted ecological research on the dynamics of Zika virus in its sylvatic, enzootic cycle in Africa, and characterized the evolution of the virus during its movement to and through Asia. It will be important to expand these studies of Zika virus into the Americas. Specifically, it will be critical to rigorously test the association between microcephaly and maternal infection with Zika virus, monitor viral evolution in the Americas, characterize all routes of virus transmission, including the contribution of vectors other than
Ae. aegypti, investigate mechanisms of pathogenesis, and conduct surveillance in wildlife, particularly primates, to ascertain whether the virus has the potential to establish a spill-back American enzootic cycle.